As a general rule, the retention times of known small molecule fluorescent probes inside cells is relatively low.31 However, several pH probes have been internalized into cancer cells as the result of a tumour-targeting entity and used for the selective labelling of cancer cells or activate chemotherapeutics agents in cancer cells, such as HIα1,32,33 NQO1,34,35 H2S,36,37 and others.38,39 However, these probes are specific to special of cancer cell phenotypes. Here, NQO1 is linked to cancer.